The invention relates generally to turbine systems, and more particularly to, low emission turbine systems and methods.
Various types of gas turbine systems are known and are in use. For example, aeroderivative gas turbines are employed for applications such as power generation, marine propulsion, gas compression, cogeneration, offshore platform power and so forth. Typically, the gas turbines include a compressor for compressing an air flow and a combustor that combines the compressed air with fuel and ignites the mixture to generate an exhaust gas. Further, the exhaust gas is expanded through a turbine for power generation.
Typically, the combustors for such systems are designed to minimize emissions such as NOx and carbon monoxide (CO) emissions. In certain traditional systems, lean premixed combustion technology is employed to reduce the emissions from such systems. Typically, NOx emissions are controlled by reducing the flame temperature in the reaction zone of the combustor. In operation, low flame temperature is achieved by premixing fuel and air prior to combustion. Further, certain gas turbine systems are utilized using high levels of airflow, thereby resulting in lean fuel mixtures with a flame temperature that is low enough to reduce the formation of NOx. However, because lean flames have a low flame temperature, they result in high CO emissions. Further, the window of operability becomes very small for such combustors and the combustors are required to be operated away from the lean blow out limit. As a result, it is difficult to operate the premixers employed in the combustors outside of their design space.
Moreover, when sufficiently lean flames are subjected to power setting changes, flow disturbances, or variations in fuel composition, the resulting equivalence ratio perturbations may cause loss of combustion. Such a blowout may cause loss of power and expensive down times in stationary turbines.
Certain other systems employ post combustion control techniques to control the emissions. For example, selective catalytic reduction (SCR) techniques may be utilized as an add-on NOx control measure. In an SCR process, a gaseous or liquid reductant such as ammonia may be directly injected into the exhaust gas from the turbine, which is then passed over a catalyst to react with NOx. The reductant converts the NOx in the exhaust gas to nitrogen and water. However, incorporation of additional components, such as a catalytic reactor for the SCR process, is a challenge, due to costs and the added complexity of such systems.
Accordingly, there is a need for a turbine system that has reduced emissions. Furthermore, it would be desirable to provide combustion technologies that enhance the overall efficiency of the turbine system without correspondingly increasing thermal NOx formation.